Micro-Electromechanical Systems (MEMS), also referred to as micromachines, are very small, electrically driven mechanical devices fabricated using semiconductor device or integrated circuit (IC) manufacturing technologies. One particularly useful type of MEMS is a reflective spatial light modulator (SLM) that uses electrical signals to move micromechanical structures to modulate light incident thereon. The incident light can be modulated in intensity, phase, polarization or direction. MEMS spatial light modulators are increasingly being developed for use in various applications, including display systems, optical information processing and data storage, printing, and maskless lithography. In a maskless lithography system, a mask and/or reticle is replaced by a dynamic direct writing process using a high power light source, such as a laser, and spatial light modulators. Maskless lithography speeds up IC design cycle times and reduce cost, particularly with respect to design changes, which would previously require one or more new masks to be made for each design revision. Similar systems may also be used in patterning masks.
One problem with conventionally packaged MEMS spatial light modulators in general, and those used in maskless lithography systems in particular, is that the high power lasers used can volatilize contaminates and materials in the MEMS package, which can build up on surfaces of the SLM, reducing the reflectivity and operating life of the SLM. Heretofore attempts to address these problems have focused on thoroughly evacuating and hermetically sealing the MEMS package in which the SLM is contained. However, this approach has not been satisfactory.